Beaver dams keep streams cool and protect sensitive fish

Previous studies suggested that these dams warm the water, for example, by expanding its surface area and cutting its flow speed. But the opposite may in fact be the case, says Nicholas Weber at Eco Logical Research Inc in the US.

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Weber’s team monitored stream temperatures at 23 sites along 34 kilometres of Bridge Creek in Oregon for eight years. The number of beaver dams there increased over this period from 24 to 120. The team looked at temperature differences between an upstream site with no beaver activity and downstream areas before and after the dam proliferation. By the end of the eight years, maximum daily temperatures downstream had dropped by 2.6°C on average, though it’s not clear how the dams lead to this (PLoS One, doi.org/b692).

“These results suggest that beaver relocation projects could be used to mitigate the impact of human-induced thermal degradation that may threaten sensitive cold-water fish species,” says Weber.

This article appeared in print under the headline “Rivers stay cool thanks to beavers”